Roof antenna with improved casing

Abstract

A roof antenna capable of receiving three kinds of bands, i.e., a FM radio band, an AM radio band, and a wireless-telephone band, includes an antenna element 10 having a structure that a conductor 15 winds around the insulator 16 in the form of a coil. A molded portion 14 is formed at the bottom of the antenna element, in which a trap coil is inserted. The electric length from the antenna top 11 to the internal metal fitting 17 at the lower end of the antenna element 10 is about a quarter of a FM radio wave. The electric length from the internal metal fitting 17 to the lower end of the trap coil 12 is about a quarter of a wireless telephone wave. A cover 19 supporting a basal part of the antenna element installs the first substrate 20 and the second substrate 21. The first substrate 20 and the second substrate 21 have a matching circuit, branching filters, and amplifiers.

What is claimed is: 
     
       1. A roof antenna capable of receiving three kinds of bands, comprising: an antenna element having a trap coil in the middle thereof; and   an antenna case, fixed on the roof of a car, including a branching filter means, amplifiers, and a mixer therein,   wherein said antenna element is constituted so that an electric length from a bottom end of said antenna element to the trap coil is resonant with signals having a first frequency, an electric length of the whole antenna is resonant with signals having a second frequency, and an electric length of the whole antenna element receives signals having a third frequency;   said branching filter means branches and outputs said signals having the first frequency from three kinds of bands;   said signals having the second frequency and said signals having the third frequency branched by said branching filter means are amplified respectively by said amplifiers; and   said amplified signals having the second frequency and the third frequency are mixed by said mixer and output from said antenna case.   
     
     
       2. A roof antenna capable of receiving three kinds of bands according to claim 1, wherein said branching filter means, said amplifiers, and said mixer are installed in said antenna case having a capacity of not more than about 30 cc. 
     
     
       3. A roof antenna capable of receiving three kinds of bands according to claim 1, wherein said antenna case includes at least two substrates, and wherein said branching filter means, said amplifiers and said mixer are mounted on said at least two substrates. 
     
     
       4. A roof antenna capable of receiving three kinds of bands comprising: an antenna element having a trap coil in the middle thereof; and   an antenna case having a portion for fixing said antenna element, said antenna case installing a substrate comprising a branching filter means, amplifiers and a mixer, and being fixed on the roof of a car,   wherein said antenna element is constituted so that an electric length from a bottom end of said antenna element to said trap coil is resonant to signals having a first frequency, an electric length of the whole antenna is resonant with signals having a second frequency, and an electric length of the whole antenna element is resonant with signals having a third frequency; and   said antenna case comprises a cover and a base;   a metal fitting having a depression is fixed substantially watertight at the top portion of said cover so that said depression is concave toward an outside of said antenna case;   said metal fitting has an internal engaging portion at the bottom thereof; and   a metal connecting piece is electrically connected with said substrate fixed to said base;   an external engaging potion is formed at one end of a metal connecting piece by making cuts in radial directions to form tongues bent downward; and:   said cover is pressed to insert said internal engaging portion of said metal fitting for connecting the antenna element into said external engaging portion so that said metal fitting for connecting the antenna element is electrically connected to said substrate;   said branching filter means branches and outputs said signals having the first frequency from three kinds of bands;   said signals having the second frequency and said signals having the third frequency branched by said branching filter means are amplified respectively by said amplifiers; and   said amplified signals having the second frequency and the third frequency are mixed by said mixer and output from said antenna case.   
     
     
       5. A roof antenna capable of receiving three kinds of bands according to claim 1 or 4, wherein said signals having the first frequency is for a wireless telephone band, said signals having the second frequency is for a FM radio band, and said signals having the third frequency is for an AM radio band. 
     
     
       6. A roof antenna capable of receiving three kinds of bands according to claim 5, wherein said branching filter means, said amplifiers, and said mixer are separately fixed on a plurality of substrates installed in said antenna case. 
     
     
       7. A roof antenna capable of receiving three kinds of bands according to claim 6, wherein said cover has a plurality of notches each having a shape of ring, said substrates abutting on said notches so that said substrates are installed nearly parallel to said base. 
     
     
       8. A roof antenna capable of receiving three kinds of bands according to claim 1 or 4, wherein said branching filter means, said amplifiers, and said mixer are separately fixed on a plurality of substrates installed in said antenna case. 
     
     
       9. A roof antenna capable of receiving three kinds of bands according to claim 8, wherein said cover has a plurality of notches each having a shape of ring, said substrates abutting on said notches so that said substrates are installed nearly parallel to said base. 
     
     
       10. A roof antenna capable of receiving three kinds of bands according to claim 4, wherein said branching filter means, said amplifiers, and said mixer are installed in said antenna case having a capacity of not more than about 30 cc. 
     
     
       11. A roof antenna capable of receiving three kinds of bands comprising: an antenna case fixed on the roof of a car; and   an antenna element capable of receiving three kinds of bands, fixed to said antenna case;   wherein said antenna case comprises a cover and a base;   a metal fitting portion for connecting the antenna element, having a depression is fixed watertightly at the top portion of said cover so that said depression faces the outside, said metal fitting having an internal engaging portion at the bottom thereof;   a metal connecting piece is electrically connected with a substrate fixed to said base;   an external engaging portion is formed at one end of said metal connecting piece by making cuts in radial directions so as to have tongues bent downward; and   said cover is pressed to insert said internal engaging portion of said metal fitting for connecting the antenna element to said external engaging portion so that said metal fitting for connecting the antenna element is electrically connected to said substrate.   
     
     
       12. A roof antenna capable of receiving three kinds of bands according to claim 11, wherein said antenna element is constituted so as to receive signals having frequencies for a wireless telephone band, a FM radio band, and an AM radio band.